1. Field of the Invention
The present invention relates to a method for inserting slide frames or film strips into the pockets of a two-layer film jacket open on one side, the pockets being partitioned from each other by transverse seams, preferably transverse weld seams, and to an apparatus for carrying out said method.
2. Description of Prior Art
Methods for inserting slide frames into the pockets of a film jacket are known from the German laid-open print 37 08 880 (see corresponding U.S. Pat. Nos. 4,848,576 and 4,995,221) and from the published European patent application 228 536. In the known methods, slide frames are inserted into the pockets of a two-layer continuous film jacket being open on one side, said pockets being partitioned from each other by transverse weld seams. The pockets extend in the transverse direction of the film. Each pocket is adapted to receive several slide frames successively. The slide frames are successively pushed through the opening at one side of the film jacket. Each pocket is provided with apertures in one of the two films, which are arranged at a distance corresponding to that of the slides so that each slide can be taken out thereof individually. The details are described in the German laid-open print 37 08 880; reference is explicitly made to said prepublication (the disclosures of U.S. Pat. Nos. 4,848,576 and 4,995,221 are incorporated herein by reference). After the filling of a pocket, the film jacket is transported further in the longitudinal direction of the film, i.e. transversely to the direction of the pockets, to the next pocket to be filled. I.e., the film jacket is transported by a distance corresponding to the distance between the pockets. For permitting an exact positioning of the next pocket to be filled, in the known solution, identification marks are imprinted consisting of colored, e.g. black, bars. Said marks are detected by an optical sensor. The marks are arranged spaced apart from each other at the distance of the pockets. They can, for instance, respectively align with a transverse weld seam.
German utility model 72 24 072 discloses a method for inserting film strips into the pockets of a film jacket, which is operated in substantially the same manner. The difference lies only in the fact that, instead of slide frames, film strips are inserted into the pockets of the film jacket.
Hence, in the known solutions the positioning of the film jacket is controlled by means of imprinted marks which are applied to the individual pockets at a constant distance. The film jacket is transported further after the filling of a pocket until the optical scanning device detects the location of the next mark and thus of the next pocket.
Disadvantageously, in the known methods, there exist unavoidable process tolerances between the layers of the pockets and the marks. The application of marks is only possible within certain unavoidable process tolerances. Furthermore, the printing process represents an additional work cycle. Consequently, in addition to producing the pockets, the imprinted marks also have to be produced in a separate work cycle. Finally, also, the imprinting of the film is difficult. In case of a too low degree of application of color, there may be problems in detecting the color marks and thus in positioning the film jacket.
From the German published examined application 21 66 340, there is known a feed device for a film web having a sequence of pockets. This feed device feeds the pockets to a work station so that they are suitably positioned. In the feed direction prior to the work station, there is provided a cam which is reciprocably movable in parallel to the feeding direction. The cam engages with the pockets during advancing and is pivotable out of engagement during retraction. To permit wrinkle-free advancing of a flat pocket band consisting of soft film in such an apparatus, a friction band is provided for advancing a pocket made of a longitudinally folded film web by means of transverse connections. The friction band is arranged between the cam acting upon the transverse connections and the work station. The friction band acts upon the pocket band. In the advance cycle, it can be driven at a higher speed than the cam. The tensile force transmitted from the friction band to the pocket band under slip is smaller than the force required for advancing the pocket band. In the German published examined application 21 66 340 the cam is not used for detecting the position of the next transverse connection in the film web but for advancing the film web by one pocket width, i.e. for bringing the next pocket of the film web in the working position.